1. Field of the Invention
The present invention relates to an evaporated fuel treatment apparatus which has a canister for adsorbing an evaporated fuel produced in a fuel tank and which treats the evaporated fuel and relates to a control method for a control valve provided at a communication path (a vapor path) between the fuel tank and the canister of the evaporated fuel treatment apparatus, and more particularly, relates to a method of detecting a failure in the control valve.
2. Description of the Related Art
Conventional evaporated fuel treatment apparatuses cause a canister to adsorb an evaporated fuel in order to reduce the pressure in a fuel tank, thereby preventing the evaporated fuel produced in the fuel tank from being released to the atmosphere at the time of fuel charging (see, for example, JP 2001-140705A).
JP 2001-140705A discloses an evaporated gas suppressing apparatus which has a control valve provided at a communication path between a fuel tank of a vehicle such as an automobile and a canister for adsorbing an evaporated fuel (a vapor) produced in the fuel tank, opens the control valve in a condition in which the pressure inside the fuel tank becomes higher than a predetermined pressure in a status of fueling and while the vehicle is running, and closes the control valve while the vehicle is at rest.
According to the conventional evaporated fuel treatment apparatuses, the control valve is provided at a vapor path between the fuel tank and the canister, the control valve is opened prior to fuel charging in order to allow the canister to adsorb the evaporated fuel in the fuel tank through the control valve, thereby reducing the pressure inside the fuel tank. Reduction of the pressure prevents the evaporated fuel from being released to the atmosphere during fueling.
According to the conventional evaporated fuel treatment apparatuses, the canister becomes able to adsorb the evaporated fuel upon opening of the control valve. When a driver opens a filler cap after the pressure difference between the pressure inside the fuel tank and the atmospheric pressure becomes equal to or smaller than a predetermined pressure difference, it is possible to prevent the evaporated fuel from being released to the atmosphere. At this time, it is necessary for the driver to wait to open the filler cap until the pressure difference between the pressure inside the fuel tank and the atmospheric pressure becomes equal to or smaller than a predetermined pressure difference. It is desirable that the waiting time for opening the filler cap should be short to such an extent that the driver does not feel that the driver is forced to wait.
In the meantime, vehicles like plug-in hybrid vehicles that do not run an engine for a long time normally close the control valve so that the evaporated fuel from the fuel tank is not adsorbed by the canister. When the control valve is kept closed for a long time, the control valve may be seized because of a gum element produced when a resin part of the control valve is dissolved by a liquid.
Accordingly, an opening/closing operation of the control valve can be considered in the method disclosed in JP 2001-140705A in order to detect a seizing failure of the control valve. However, an opening/closing operation of the control valve causes the canister to adsorb the evaporated fuel, so that in the case of a vehicle which does not run the engine for a long time like a plug-in hybrid vehicle, such a vehicle needs a canister with a further large capacity.